Field of the Invention
The present invention relates to an image forming apparatus configured to transfer a toner image carried on an image carrier to a recording medium carried on a transfer belt.
Description of the Related Art
Hitherto, there is widely known an image forming apparatus configured to pass a recording medium through a transfer portion while carrying the recording medium on a transfer belt and to transfer a toner image carried on an intermediate transfer belt, i.e., one example of an image carrier, to the recording medium carried on the transfer belt in a transfer portion as disclosed in Japanese Patent Application Laid-open No. 2012-128228.
If the recording medium has low rigidity like a thin sheet or has been already waving-deformed, there is a case when the recording medium is wrinkled in passing through the transfer portion to transfer the toner image in the image forming apparatus using the transfer belt.
Then, there is proposed an arrangement in which an outer circumferential surface of a transfer roller formed into a shape of an inversed crown is brought into pressure contact with the image carrier through an intermediary of the transfer belt. As disclosed in Japanese Patent Application Laid-open No. Hei. 7-225523, a conveying speed of end parts in a direction of axis of rotation of the transfer roller whose outer circumferential surface is formed into the inversed crown shape increases more than a conveying speed of a center part thereof, a rear end side of the recording medium passing through the transfer portion is spread in the direction of axis of rotation. This arrangement might be expected to exhibit an effect of smoothing wrinkles on both end parts and rear end portion in a conveying direction of the recording medium and to reduce wrinkles otherwise generated on the both end parts and the rear end portion in the conveying direction of the recording medium.